title: Unusual base pairing during the decoding of a stop codon by the ribosome.
abstract: During normal translation, the binding of a release factor to one of the three stop codons (UGA, UAA or UAG) results in the termination of protein synthesis. However, modification of the initial uridine to a pseudouridine (Ψ) allows efficient recognition and read-through of these stop codons by a transfer RNA (tRNA), although it requires the formation of two normally forbidden purine-purine base pairs. Here we determined the crystal structure at 3.1 Å resolution of the 30S ribosomal subunit in complex with the anticodon stem loop of tRNA(Ser) bound to the ΨAG stop codon in the A site. The ΨA base pair at the first position is accompanied by the formation of purine-purine base pairs at the second and third positions of the codon, which show an unusual Watson-Crick/Hoogsteen geometry. The structure shows a previously unsuspected ability of the ribosomal decoding centre to accommodate non-canonical base pairs.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors.forename: Israel S
authors.initials: IS
authors.lastname: Fernández
authors.forename: Chyan Leong
authors.initials: CL
authors.lastname: Ng
authors.forename: Ann C
authors.initials: AC
authors.lastname: Kelley
authors.forename: Guowei
authors.initials: G
authors.lastname: Wu
authors.forename: Yi-Tao
authors.initials: YT
authors.lastname: Yu
authors.forename: V
authors.initials: V
authors.lastname: Ramakrishnan
mesh_terms: D000926:Anticodon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020029:Base Pairing; D001483:Base Sequence; D018388:Codon, Terminator / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D011560:Pseudouridine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012362:RNA, Transfer, Ser / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054680:Ribosome Subunits, Small, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000926:Anticodon; D018388:Codon, Terminator; D012362:RNA, Transfer, Ser; D011560:Pseudouridine